In many crops, hybrids (F1) cross-breeded inter-species or inter-lines of species represent heterosis. These hybrids have high adaptability to environmental changes and are therefore resistant to plant diseases and environmental stresses. They can also be superior to their parents in certain desirable agricultural traits. Therefore most vegetable seeds cultivated and sold by seed companies is F1 hybrids.
Because reproduction mechanisms in higher plants are very complicated, it is not easy to obtain pure hybrid seeds in large quantities without self-pollination of the parent plant taking place. In order to solve the problem and to enhance the rate of outbreeding, an artificial pollination method has been used for a long time. The artificial pollination method involves the removal of anthers or tassels from the female parent plant and artificial fertilization with pollen from the male parent plant, either manually or mechanically.
However, such an artificial pollination method is labor intensive and not altogether reliable as it is possible that some female plants may escape the detasseling process in some cases. In addition, this approach is not easily applicable to species in which the male and female floral organs are very small.
Meanwhile, in order to solve the problems of artificial pollination, another approach is also known. The approach involves the production of a male sterile line using the incompatibility allele or the male sterility gene that represses the development of pollen. For example the cytoplasm male sterile line of some crops is used for cross-breeding. However, again such a technique may cause side effects such as degradation of disease resistance and is not wholly reliable.
Another approach is to induce artificial mutation and to select male sterile lines. Chemical methods that degrade the fertility of plants are also known. However, there are some limitations in usage, since these methods lack stability and the mechanisms are not understood.
Recently molecular biological studies searching for the mechanism of male sterility, inserting the gene only inducing male sterility into the genome of a plant and breeding new plant species have been conducted. It is very effective in inducing male sterility with maintaining the desirable traits of species to use such genetic manipulation techniques.
However, if the gene inducing male sterility is inserted into the genome of a plant and the expression of the gene starts from the early developmental stages of plant, it may affect adversely the growth of the plant and the desirable agricultural traits of the plant species. Therefore if a promoter region (regulating site of a gene) can regulate the expression of the gene that inhibits the growth or germination of the pollen, male sterility can be induced without affecting the development and growth of the plant.
In order to effectively produce male sterile crops having desirable agricultural traits, some researchers have studied pollen-specific promoter regions and the genetic structure comprising the promoter regions (WO 96/17945; KR Patent No. 0278819, Hyun ook Kim, Production of male sterile Tobacco Plants Using an Anter-Specific Promoter Recombinant, thesis for a doctorate, Seoul National University, 1995).
A need exists for novel promoters that have specific roles in particular organs and at particular developmental stages, such as in mature flowers to regulate male sterility.
An object of the present invention is to provide a novel pollen-specific promoter that regulates the expression of a gene only in the pollen tissue, particularly in mature pollen tissue, thereby being useful as means of production of a male sterile line.
Another object of the present invention is to provide a recombinant vector comprising the solely pollen-specific promoter, and a transformed plant cell using the promoter.